The present invention is directed to the manufacture of composite as well as super plastic forming and bonding of thin sheet metal components.
Composite components are typically produced by impregnating a fibrous material such as fiberglass with a resin matrix or bonding medium such as thermoplastic or thermocuring resin, or forming and bonding sheets of thermoplastic material together or in layers to form parts. This resin impregnated material is subsequently subjected to an elevated pressure and temperature to compress the material and form or cure the resin matrix or bonding medium to thereby produce the composite/bonded component. Bonded metal components are formed by shaping the thin metal sheets and placing adhesive or bonding material between the sheets then elevating the temperature whilst maintaining a holding pressure or clamping force to ensure an adequate bond. In each case the material needs to be compressed to expel excess air and resin from within the composite lay-up or metal bond to cure the laminate into a solid layer or bond the solid laminates together to form a final part. Lightweight components of high strength can be produced by this method making such components particularly suitable for aircraft, automotive and marine applications.
The Applicant has developed a system for producing such composite components as described in International Patent Application No. PCT/AU95/00593, details of which are incorporated herein by reference. The described system uses a pair of pressure chambers respectively providing a mold surface and a backing surface. The mold surface may be provided by a floating rigid or semi rigid mold forming a wall of one of the pressure chambers. The backing surface may be provided by either a second cooperating floating rigid or semi rigid mold, or a vacuum bag, or a resiliently deformable bladder forming a wall of the other pressure chamber. A composite lay-up may be made up of a layer of resin impregnated material overlaid by a peel cloth and a bleeder cloth which can be located between the mold and backing surfaces. Once the composite lay-up are placed in position, fluid at elevated pressure and temperature is circulated through each pressure chamber to thereby both compress the lay-up and form or cure the resin matrix or bonding medium. Alternatively, layers of material may be initially laid in the mold to provide a laminate, and Resin Transfer Molding or Resin Film Infusion used to introduce the resin to the laminate thereby allowing forming of the part. The circulation of the fluid provides for very uniform curing of the component with fast cycle times, heat up and cool down and efficient energy use. Furthermore, in a preferred arrangement of this system, equal pressures can be applied to opposing sides of the composite lay-up because fluid at the same pressure is circulated through each pressure chamber. The resultant composite component has excellent material uniformity when compared with composite components manufactured with other known composite production processes.
The Applicant has also developed a system for producing, repairing, forming, and bonding both composite and metal components in International Patent Application No. PCT/AU01/00224 using at least one pressure chamber having a displaceable abutment face, with fluid being circulated at an elevated temperature and pressure.
In all of the systems, developed by the Applicant, the common principle of operation is the use of circulating fluid at elevated temperature and pressure to effect the curing process. The advantage of using circulating fluid as a heating (or cooling medium) is the ability to transfer heat rapidly and evenly to the area being heating. In practice, this results in curing times for the production composite products that are substantially shorter than that possible with conventional autoclave production processes. This is because of the higher heat transfer rates in fluid compared with air (i.e., typically 22 times greater with water). The result is substantially greater production speeds and lower overall production costs per unit.
Another advantage in using circulating fluid is that the heat is transferred more evenly to the lay-up with no “hot spots” as can occur using autoclave or other heating methods.
The Applicant's systems also provide relatively uniform pressure over the lay-up because of their use of circulating fluid at elevated pressure. Furthermore, in the arrangements where pressure is applied to opposing sides of a lay-up, the pressure can be balanced such that it is unnecessary to use apparatus having high structural strength to support any applied heavy loads.
Furthermore, the present invention can utilize a “balanced density” effect which enables large panels and components to be produced. Details of this effect will be hereinafter further described.
While the composite component production system described in International Patent Application No. PCT/AU95/00593 is in use, it is not possible to prepare the next composite lay-up until the composite component currently being manufactured has been cured or formed. Furthermore, it is not possible to readily change molds to produce a different composite component as this requires the floating rigid or semi rigid mold to be detached from the pressure chamber and to be replaced with another rigid or semi rigid mold of a different configuration. With the mold fixed in the wall of the pressure chamber it is difficult to maneuver the mold to get access to the mold for example to place the composite materials into the mold.
In addition it is difficult to work on the mold to place the stiffeners into the part whilst it is in the pressure cell with the pressure chambers surrounding it. It is possible to take the composite part out of the mold then place it in a jig and fit the stiffeners e.g. ribs, bulkheads, strongbacks etc. However this is not preferable as the composite component is not generally rigid and tends to flex until all stiffeners are in position. It is therefore preferable to place all stiffeners and complete all secondary processes before removing the part from the mold. In this way maximum dimensional accuracy is ensured.
Also in some circumstances it is necessary or preferable to have split molds to release a part from the mold. This is difficult to accommodate within the present process without split pressure chambers and sophisticated locking mechanisms in the walls of the mold to hold the molds together to ensure no loss of fluids.
Also, it is difficult to adapt the pressure chamber to produce composite components of widely different sizes because of the floating mold arrangement. This is therefore a “batch” process where it is not possible to undertake any further action until the current curing, forming procedure is completed. It would however be advantageous to be able to have a composite production system that allows for a “semi-continuous” process where at least a part of the manufacturing procedure can be done even when the system is currently compacting, curing and or forming a composite or bonded metal component while at the same time maintaining the quality of the component produced by such a system. It would also be advantageous to be able to produce a variety of different components and molds for those components themselves radically decreasing the cost of tooling without having to alter the basic configuration of the sealed pressure chambers and the release of fluid from the system. This will facilitate the introduction of such a system to mass production applications because of the improved time and production efficiency.